Growth of a single-crystal region of a III-V compound on a single-crystal silicon substrate

ABSTRACT

A method for growing a single-crystal region of a III-V compound on a surface corresponding to a crystallographic plane of a single-crystal silicon substrate, including the steps of growing by epitaxy on the substrate a single-crystal germanium layer; etching in a portion of the thickness of the germanium layer an opening, the bottom of which corresponds to a single surface inclined with respect to the cristallographic plane or to several surfaces inclined with respect to the cristallographic plane; and growing the single-crystal III-V compound on the bottom of the opening.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of growth of a single-crystalregion of a III-V compound on a single-crystal silicon substrate. Thepresent invention also relates to the device obtained by the presentmethod. The present invention especially applies to the forming of asingle-crystal region of a binary compound of gallium arsenide (AsGa) ona single-crystal silicon substrate on which are formed othersemiconductor components.

2. Discussion of the Related Art

III-V compounds are currently used to form optoelectronic devices, forexample, solar cells, lasers or diodes, or to form fast circuits.

It is known to grow, by epitaxy, a layer of a binary AsGa compound on asolid germanium substrate, germanium and AsGa having a similar meshparameter. However, when AsGa is grown on an oriented single-crystalgermanium substrate, the orientation of which is for example (100), theobtained AsGa layer exhibits a polycrystalline structure. Indeed, AsGais a binary compound which may start its growth on an As plane or on aGa plane. On the (100) oriented germanium surface, the AsGa nucleationmay start from any point of the surface according to an As plane or to aGa plane. AsGa grains, which have started, some from a Ga surface, theothers from an As surface, tend to grow and form, when they join, grainjoints. Such grain joints are called antiphase domains (APD) andcorrespond to defective regions which are undesirable whenoptoelectronic devices or fast circuits are desired to be formed in theAsGa layer.

To avoid forming of grain joints, the surface of the solidsingle-crystal germanium is generally altered to form steps on the edgesof which, with adapted deposition conditions, it is possible to have theAsGa nucleation start preferentially from the same initial As or Gaplane. Optimally, the solid germanium surface is mechanically worked,for example, by polishing, to obtain a surface inclined by approximately6° with respect to the (100) growth planes.

There currently is a need for III-V compound single-crystal regions, inparticular of AsGa, on a silicon wafer to integrate optoelectronicdevices or fast circuits formed at the level of the AsGa regions withthe other semiconductor components formed on the wafer.

For this purpose, portions of a single-crystal AsGa layer previouslyformed on solid germanium are currently placed on the silicon wafer.

Indeed, even if it is known to directly grow a single-crystal germaniumlayer of a few micrometers on a single-crystal silicon wafer, theobtained single-crystal germanium keeps the crystalline informationprovided by the single-crystal silicon and is thus oriented, most oftenaccording to orientation (100) which corresponds to the usualorientation of silicon wafers used in microelectronics. For the samereasons as those discussed previously, if a III-V compound is grown byepitaxy on the germanium surface formed on the silicon wafer, theobtained structure is polycrystalline. Now, no simple means arecurrently known to mechanically work a germanium layer of a fewmicrometers and form surfaces inclined by 6° on which a single crystalof the III-V compound could grow.

Further, when germanium is grown on a “de-oriented” single-crystalsilicon wafer, that is, the surface of which would have been polishedaccording to a plane inclined with respect to the silicon growth planes,it can be observed that the germanium tends to return to a conventionalorientation, and not to keep the de-oriented character of silicon.

SUMMARY OF THE INVENTION

The present invention aims at growing single-crystal regions of III-Vcompounds directly on a single-crystal silicon wafer.

Another object of the present invention is to obtain a growth method ofsingle crystal regions of III-V compounds on a single-crystal siliconwafer which is compatible with conventional integrated circuitmanufacturing processes.

To achieve these and other objects, the present invention provides amethod for growing a single-crystal region of a III-V compound on asurface corresponding to a crystallographic plane of a single-crystalsilicon substrate, comprising the steps of growing by epitaxy on thesubstrate a single-crystal germanium layer; etching in a portion of thethickness of the germanium layer an opening, the bottom of whichcorresponds to a single surface inclined with respect to said surface orto several surfaces inclined with respect to said surface; and growingthe single-crystal III-V compound on the bottom of the opening.

According to an embodiment of the present invention, the single-crystalsilicon substrate has orientation (100) and said inclined surface(s) is(are) inclined by an angle of substantially from 5 to 7 degrees withrespect to said surface.

According to an embodiment of the present invention, the single-crystalsilicon substrate has orientation (100) and the bottom of the openingcomprises two surfaces inclined by substantially from 5 to 7 degreeswith respect to said surface.

According to an embodiment of the present invention, the method furthercomprises the step of growing on the single-crystal silicon substrate atleast one layer of a silicon and germanium alloy on which the germaniumlayer is grown.

According to an embodiment of the present invention, the method furthercomprises the step of growing an oxide layer on the germanium layer andof etching said oxide layer to form a raised area on said oxide layer,the shape of the surface of said raised area being transferred byetching into the germanium layer.

According to an embodiment of the present invention, the thickness ofthe germanium layer separating the bottom of the opening and thesingle-crystal silicon substrate is greater than 300 nanometers.

According to an embodiment of the present invention, the opening has across-section with an area of a few tens of square micrometers.

According to an embodiment of the present invention, the III-V compoundis gallium arsenide.

The present invention also provides a device comprising a single-crystalsilicon substrate comprising a surface corresponding to acrystallographic plane covered with a single-crystal germanium layer, inwhich the germanium layer comprises at least one opening with a depthsmaller than the thickness of the germanium layer, the bottom of theopening corresponding to a single surface inclined with respect to saidsurface or to several surfaces inclined with respect to said surface,said opening containing a III-V compound.

According to an embodiment of the present invention, an electroniccomponent is formed in the III-V compound.

The foregoing objects, features and advantages of the present invention,will be discussed in detail in the following non-limiting description ofspecific embodiments in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1D show cross-sections of the structure which is desired tobe obtained at successive steps of a first embodiment according to thepresent invention; and

FIGS. 2A to 2D show cross-sections of the structure which is desired tobe obtained at successive steps of a second embodiment according to thepresent invention.

DETAILED DESCRIPTION

The present description will be made in the case where the III-Vcompound is gallium arsenide.

FIG. 1A shows a cross-section of a portion of a single-crystal siliconwafer 10 on which has been grown by epitaxy a single-crystal germaniumlayer 12 of a thickness that can be greater than one micrometer. Thesingle-crystal silicon is oriented, for example, according toorientation (100) which is the orientation usually used in semiconductormanufacturing processes. Single-crystal germanium 12 reproduces thecrystalline information of single-crystal silicon wafer 10 and exhibitsan orientation direction similar to that of silicon.

According to an alternative of the present invention, single-crystalsilicon wafer 10 may comprise the upper layer of asubstrate-on-insulator type structure (SOI). Germanium layer 12 mayfurther be formed by any known method and, in particular, may comprise asuccession of layers of a silicon and germanium alloy, SiGe, where theatomic concentration in germanium increases from zero to 100% as it ismoved away from silicon wafer 10.

For such a single-crystal germanium layer 12, it is known that beyond asufficient thickness, the surface density of defects, especially ofemergent dislocations, is small, typically under 106 cm-2. Referencenumeral 13 represents the portion of germanium layer 12 close to siliconwafer 10 for which the surface density of defects is greater thanacceptable values. Portion 13 of germanium layer 12 typically has athickness on the order of 300 nanometers.

In FIG. 1B, an opening 14 has been etched in germanium layer 12, thedimensions of which are slightly greater than the dimensions of theactive AsGa area which is desired to be formed. As an example, thecross-section of opening 14 may be a square or a rectangle, having sidesmeasuring less than 10 micrometers. Opening 14 may belong to a set ofopenings simultaneously formed in germanium layer 12, and each of whichis associated with an AsGa region which is desired to be formed. Theetch used may be a dry etch performed after deposition of a resist ongermanium layer 12, insolation of the resist to define the distributionof openings 14 at the locations where active areas of the III-V compoundare desired to be formed, followed by the resist development.

Bottom 16 of opening 14 obtained with such an etch is typicallysubstantially flat and corresponds to a (100) germanium growth plane.The depth of opening 14 is smaller than the total thickness of germaniumlayer 12 decreased by the thickness of portion 13 to ensure the absenceof emerging dislocations on bottom 16.

FIG. 1C shows the structure obtained once bottom 16 of opening 14 hasbeen altered. This may be obtained by modifying the parameters of areactive ionic etch to favor redepositions at the bottom off opening 14.Two roof-shaped inclined surfaces 18, 20 are obtained, each surface 18,20 being generally inclined by an angle of approximately 6° with respectto an orientation plane (100) of the germanium. Each surface 18, 20 isformed in practice of a succession of “steps” at the scale of atomicsilicon planes.

According to an alternative, a single surface inclined by 6° withrespect to a (100) orientation plane of the germanium, or a recess withtwo surfaces inclined by 6° with respect to a (100) orientation plane ofthe germanium may be formed.

In FIG. 1D, AsGa has been grown on inclined surfaces 18, 20 to form asingle-crystal AsGa region 22. The thickness of region 22 may besufficiently high, for example, greater than 1 micrometer, for thealtered shape of bottom 16 of opening 14 to be substantially smoothed atthe surface of region 22. Preferably, the AsGa is made to grow above thesurface of germanium layer 12 and the growth is followed by a leveling,for example, by chem-mech polishing. An optoelectronic device or a fastcircuit can then be defined in region 22 according to the desiredapplication.

FIGS. 2A to 2D illustrate the steps of a second embodiment of thepresent invention.

According to the second embodiment, as shown in FIG. 2A, single-crystalgermanium layer 12 formed on single-crystal silicon wafer 10 is coveredwith a silicon oxide 24 of a thickness for example on the order of 200nm, surface 25 of which is substantially planar.

In FIG. 2B, silicon oxide layer 24 has been etched to form a non-planararea 26 at the level of the location where an active AsGa area isdesired to be formed. Non-planar area 26 may, for example, have theshape of a roof with two inclined sides 27, 28, each side being inclinedby approximately 6 degrees with respect to the planar surface of oxidelayer 24. The roof shape may be obtained by covering silicon oxide layer24 with a mask, by forming in the mask an opening at the level of thearea to be etched, a mask island being left at the center of theopening, and by isotropically etching silicon oxide layer 24 through theopening. The presence of the island results in the forming of theinclined sides.

In FIG. 2C, silicon oxide layer 24 has been etched down to germaniumlayer 12 to only leave a raised area 30 formed of silicon oxide at thesurface of germanium layer 12. Raised area 30 reproduces the shape ofnon-planar area 26 formed at the previous step. A mask 31 has beendeposited on germanium layer 12 and raised area 30. An opening 32,formed in mask 31, exposes raised area 30, mask 31 being capable ofslightly covering the periphery of raised area 30.

In FIG. 2D, raised area 30 and single-crystal germanium 12 have beenetched through opening 32 of mask 31 by an anisotropic etch method usinga product etching substantially at the same speed the silicon oxide andthe germanium to form an opening 33 in germanium layer 12, bottom 34 ofwhich reproduces the shape of relief 30. The step of forming of thesingle-crystal AsGa region in opening 32 is identical to what has beendescribed previously.

Other III-V compounds, the direct growth of which is delicate ongermanium, for example, InAsGa, may be grown in a known manner on theAsGa layer.

The present invention has been described in the context of the formingof AsGa. Of course, the present method may be implemented for the growthof any III-V compound having a mesh parameter compatible with that ofgermanium.

The present invention has many advantages.

First, it enables forming of active areas of a single-crystal III-Vcompound on a silicon wafer.

Second, it enables forming of active areas of a single-crystal III-Vcompound having a surface area on the order of a few tens of squaremicrometers, which currently corresponds to the dimensions required toform optoelectronic devices or fast circuits.

Third, the previously-described embodiments implement techniquescurrently used upon forming of conventional integrated circuits on asilicon wafer and can thus be easily integrated in conventionalmanufacturing processes.

Of course, the present invention is likely to have various alterations,modifications, and improvement which will readily occur to those skilledin the art. In particular, in the second embodiment, the silicon oxidelayer may be replaced with nitride Si3N4 or SI—O—N type compounds.

Such alterations, modifications, and improvements are intended to bepart of this disclosure, and are intended to be within the spirit andthe scope of the present invention. Accordingly, the foregoingdescription is by way of example only and is not intended to belimiting. The present invention is limited only as defined in thefollowing claims and the equivalents thereto.

1. A method for growing a single-crystal region of a III-V compound on asurface corresponding to a crystallographic plane of a single-crystalsilicon substrate, comprising the steps of: growing by epitaxy on thesubstrate a single-crystal germanium layer; etching in a portion of thethickness of the germanium layer an opening, a bottom of whichcorresponds to a single surface inclined with respect to saidcrystallographic plane or to several surfaces inclined with respect tosaid crystallographic plane; and growing the single-crystal III-Vcompound on the bottom of the opening.
 2. The method of claim 1, whereinthe single-crystal silicon substrate has an orientation and saidinclined surface(s) is (are) inclined by an angle of substantially from5 to 7 degrees with respect to said crystallographic plane.
 3. Themethod of claim 1, wherein the single-crystal silicon substrate has anorientation and the bottom of the opening comprises two surfacesinclined by substantially from 5 to 7 degrees with respect to saidcrystallographic plane.
 4. The method of claim 1, further comprising thestep of growing on the single-crystal silicon substrate at least onelayer of a silicon and germanium alloy on which the germanium layer isgrown.
 5. The method of claim 1, further comprising the step of growingan oxide layer on the germanium layer and of etching said oxide layer toform a relief area on said oxide layer, a shape of the surface of saidrelief area being transferred by etching into the germanium layer. 6.The method of claim 1, wherein the thickness of the germanium layerseparating the bottom of the opening and the single-crystal siliconsubstrate is greater than 300 nanometers.
 7. The method of claim 1,wherein the opening has a cross-section surface area of a few tens ofsquare micrometers.
 8. The method of claim 1, wherein the III-V compoundis gallium arsenide.
 9. A method for growing a single-crystal region ofa III-V compound on a surface corresponding to a crystallographic planeof a single-crystal silicon substrate, comprising: growing by epitaxy,on the substrate, a single-crystal germanium layer; etching in thegermanium layer an opening, a bottom of the opening corresponding to asingle surface inclined with respect to the crystallographic plane or toseveral surfaces inclined with respect to the crystallographic plane;and growing the single-crystal III-V compound on the bottom of theopening.
 10. The method of claim 9, wherein the single-crystal siliconsubstrate has an orientation and said inclined surface(s) is (are)inclined by an angle of substantially from 5 to 7 degrees with respectto said crystallographic plane.
 11. The method of claim 9, wherein thesingle-crystal silicon substrate has an orientation and the bottom ofthe opening comprises two surfaces inclined by substantially from 5 to 7degrees with respect to said crystallographic plane.
 12. The method ofclaim 9, further comprising growing, on the single-crystal siliconsubstrate, at least one layer of a silicon and germanium alloy on whichthe germanium layer is grown.
 13. The method of claim 9, furthercomprising growing an oxide layer on the germanium layer and etching theoxide layer to form a relief area on the oxide layer, a shape of thesurface of the relief area being transferred by etching into thegermanium layer.
 14. The method of claim 9, wherein a thickness of thegermanium layer separating the bottom of the opening and thesingle-crystal silicon substrate is greater than 300 nanometers.
 15. Themethod of claim 9, wherein the opening has a cross-section surface areaof a few tens of square micrometers.
 16. The method of claim 9, whereinthe III-V compound is gallium arsenide.